How to generate fake Normal map from an image texture inside Blender Cycles?
I think the bump node is what you want?

Plug the BW output of the image into the hight input of the bump node. Then, feed the bump node's normal output into the normal input(s) of your shader. You can also plug raw BW images into the displacement input of the Material Output. For more reading on the bump node, check this out: How to create normal texture with node setup?